This invention relates to an improved filter apparatus for use in the control of airborne particles separated from a multi-component developer material which has been agitated in the development housing of an electrostatographic processor.
In a conventional electrostatographic printing process of the type described in Carlson's U.S. Pat. No. 2,297,691 on "Electrophotography", a uniformly charged imaging surface is selectively discharged in an image configuration, thereby forming a latent electrostatic image. That image is then developed by applying a finely divided, electroscopic coloring material, called "toner", to the imaging surface.
Sometimes the process is carried out in a "non-transfer mode", meaning that the imaging surface serves as the ultimate substrate for the toned or developed image. Favored, however, is a "transfer mode" in which the developed image is transferred to a separate substrate, such as plain paper, so that the imaging surface may be reused after any residual toner has been removed therefrom. Indeed electrostatographic printing has enjoyed outstanding commercial success, especially in plain paper xerographic copiers and duplicators.
One of the common characteristics of the electrostatographic printing process is the development step. Modern processors generally carry out that step on the fly--viz. as the imaging surface moves through a development zone. To accomplish that, they normally include a cascade or a magnetic brush development system for circulating a two component developer material along a path running from a sump, through the development zone, and then back to the sump.
Briefly, the developer used in such a development system is basically a dry mixture of toner particles with or without additives to the toner and larger, so-called "carrier" particles as described, for example, in U.S. Pat. Nos. 3,590,000, 3,819,367, and 3,900,588. In practice, the materials for the toner and carrier (or sometimes, carrier coating) components of the mixture are selected from different positions in the triboelectric series so that electrical charges of opposite polarities tend to be imparted to the toner and carrier particles when the developer components are blended together. Moreover, in making those selections, consideration is given to the relative triboelectric ranking of the materials to the end that the polarity of the normal charge for the toner particles opposes the polarity of the latent images which are to be developed. Consequently, in operation, there are competing electrostatic forces acting on the toner particles. Specifically, one set of forces tend to attract them to the carrier particles while another set of forces tends to electrostatically strip them from that portion of the developer which is brought into the immediate proximity of or actuate contact with the image bearing surface.
An electrostatographic processor configured to operate in the transfer mode additionally includes a cleaning system for removing residual toner from the imaging surface after the developed image has been transferred to, say, plain paper. Again, modern processors usually carry out the step on the fly--viz., as the imaging surface moves through a cleaning zone. For that reason, such processors typically include a cleaning blade, brush or web for mechanically removing any residual toner which may tend to adhere to the imaging surface despite the transfer step.
Experience with toner handling subsystems of the aforementioned type has demonstrated that such systems often are sources of uncontrolled and undesired emissions of toner. It is known that the principal cause of that problem is the free toner which is captured in a suspended state and blown about by the air currents to which those systems are subjected. Prior attempts in solving this problem by a controlled air flow as described for example in U.S. Pat. Nos. 3,685,485 and 3,909,864 have not been entirely successful due to the poor prefiltration through baffles and the necessity to change filters frequently. The instant invention utilizes an improved toner emissioner control system and is specifically an improvement over copending application Ser. No. 597,129 filed on July 18, 1975, and commonly assigned herewith.
Accordingly, a primary object of the present invention is to provide an improved filter apparatus for suppressing undesired emissions of airborne toner particles in a partially open housing.
Another object of the invention is to provide a simple and reliable toner emission filter device for continuously recombining airborne toner particles with a multi-component developer material flowing across the filter device.
Still another object of the invention is to construct a permanent filter for toner emission control made out of a suitable material which does not chemically react with toner particles.